during the process of masturbation you concentrate yourself entirely within the present, tricking your body with your own imagination to fulfill it's biological end. After the vinegar strokes not only have you fooled your body into believing it has fulfilled it's role, therefore leaving it with nothing to do, but your mind, sinking down from fantasy to sticky reality, fully appreciates the hollowness of your charade. So in many ways through masturbation you demonstrate the futility of your existence to both your body and your mind.